Illustrated Guide

to

Tillage Weeds

June 2014

2

TABLE OF CONTENTS

Annual meadow grass 35

Annual nettle 45

Black bindweed 38

Black nightshade 44

Charlock 20

Chickweed 25

Cleavers 41

Colt’s foot 18

Corn marigold 10

Corn spurrey 26

Deadnettle 31

Fat hen 27

Fool’s parsley 7

For-get-me-not 19

Fumitory 34

Groundsel 11

Hedge mustard 23

Hemp-nettle 30

Knotgrass 39

Mayweed 12

Mayweed, scented 13

Mouse-ear chickweed 24

Nipplewort 17

Orache 28

Pansy, field 46

Poppy, common 33

Redshank 40

Scutch grass 36

Shepherd’s purse 21

Speedwell 42

Speedwell, ivy leaved 43

Sowthistle, perennial 15

Sowthistle, prickly 14

Sowthistle, smooth 16

Sun spurge 29

Swine cress 22

Thistle, creeping 8

Thistle, spear 9

Wild oats 37

Willowherb 32

1

Guide to Identifying Tillage Weeds

…and all the idle weeds that grow,

in our sustaining corn.

William Shakespeare, King Lear

This guide has been written to help farmers, growers and students identify the

more common tillage weeds in field and garden. It contains details on 42 species

which are grouped within their families.

It’s important to be able to identify weeds particularly in the seedling stage and

in these notes the key identification features for each weed are underlined, and

also where appropriate highlighted with an arrow. There are lots of other

sources available and the ones used to compile this publication are acknowledged

at the back of the book.

Weeds have been around for as long as crops have been cultivated and as

mankind spread to new lands, he brought both crop and weed seeds with him. In

Ireland land was first brought into agricultural use by Neolithic farmers about

6000 years ago and pollen records show that both cereals and their weeds were

grown at that time. Most of our weeds originated in central and southern Europe

and migrated northwards either naturally or by human hand.

Tillage weeds are annual or perennial plants that have adapted to surviving in

ground that is constantly disturbed. To be successful, annual weeds need to

display one of two characteristics, or both: either grow fast or mark time. In

the first instance they have the ability to germinate, flower and set seed quickly

e.g. chickweed, groundsel and annual meadow grass. On the other hand some

species can stay dormant in the ground for years and germinate when the soil is

cultivated e.g. redshank, fat hen, charlock and common poppy. Perennial plants

can also cause problems for the arable farmer especially those which can

establish from root fragments e.g. colt’s foot, scutch and perennial sowthistle.

Weeds are essentially just wild flowers that have adapted to growing alongside

crops. And crops themselves can become weeds if they reoccur in subsequent

crops – these are known as volunteers. Examples include potatoes, oilseed rape

and cereals. You can divide weeds into four main groups: fast growing annuals

that are out and out arable weeds (e.g. chickweed, groundsel), hedgerow weeds

that invade from the boundary (e.g. cleavers, hedge mustard), weeds that appear

after ley is ploughed down (e.g. dock, buttercup, dandelion) and perennials (e.g.

scutch). Some weeds have such a long association with tillage that you rarely see

them other than in arable ground – fat hen and corn marigold for instance.

2

Whilst some annuals can germinate at virtually any time of the year, others have

definite times of emergence:

Spring: Redshank, black bindweed, knotgrass, orache, sun spurge

fool’s parsley, hemp-nettle, hedge mustard

Spring to autumn: Corn marigold, charlock, corn spurrey, fat hen, annual

nettle, sowthistle, for-get-me-not, mouse-ear, fumitory,

deadnettle (especially autumn)

Spring and autumn: Cleavers, ivy leaved speedwell, common poppy, field pansy

All year round: Chickweed, groundsel, annual meadow grass, mayweed,

common field speedwell, shepherd’s purse

The depth from which weeds can germinate depends upon the size of the seed:

the greater the size the greater the depth. For example groundsel and poppy

have tiny seeds and mostly germinate in the top 2 cm whilst ivy leaved speedwell

and wild oats being much larger, are capable of germinating at 10 and 20 cm

respectively. The majority of weeds germinate in the top 3 cm whilst the vast

majority (98%), germinate in the top 5 cm.

The weeds in this publication have both a Latin and a common name. Latin names

have two parts to them. Senecio vulgaris is the Latin name for groundsel:

‘Senecio’ is the genus or generic name and ‘vulgaris’ is the species or specific

name; vulgaris in Latin means ‘common’. Botanists have the annoying habit of

changing familiar Latin names and just when you get used to a name, they change

it to something different. There are two name changes since the last edition:

Persicaria maculosa (redshank) has changed to Polygonum persicaria and Elytrigia repens (scutch) is now Elymus repens; in short, they have gone back to their old

names. The scientific names used in this publication are those used in Webb’s An

Irish Flora (2012).

I have come across some unusual weeds in my

time, either as rarities or as species confined

to a particular area. Annual mercury is a

common enough wild flower in the Dublin area

but the only place I’ve seen it as an arable

weed is in fields around Kinsealy Co Dublin.

You more normally see wild turnip (Brassica rapa) growing at the side of the road but will

occasionally spot it in a tillage field. Here it’s

growing in a cabbage field near Portmarnock

(see left). Field penny cress (Thlaspi arvense)

is an unusual plant but can be found in a

number of Dublin fields especially around the

3

Rush/ Lusk area. The common name comes come the distinctively shaped fruits

that look a bit like the penny of old. I sometimes come across wild radish or

runch (Raphanus raphanistrum) in North Dublin usually in the Rush-Skerries area

– normally as a curiosity rather than as a problem. Most farmers will know that

extremely common Chenopodium species, fat hen but few would recognize its

country cousin Chenopodium rubrum, red goosefoot. You’ll most commonly find it

growing on a manure heap and the very odd time in the middle of a tillage field;

perhaps it got there from land-spread dung. Hairy bitter cress is more commonly

seen as weed in horticultural areas such as nurseries and gardens but sometimes

can become a nuisance on a field scale.

Treacle mustard (Erysimum cheiranthoides) is what I call the ‘Offaly weed’ as I

have only ever seen it growing in that county. It’s an unusual brassica weed with

small yellow flowers that’s mainly found in the centre of Ireland. Another

unusual weed from Co Offaly was thorn apple (Datura stramonium) that popped

up in a field of celery. It’s a native of North America that made its way across

to Europe. It’s more common on the Continent where it’s warmer but as the

seeds are very long lived it will occasionally occur on waste and cultivated ground

in this country. Take note that it’s a highly poisonous plant – member of the

Solanaceae.

But the oddest weed I ever met was dodder (Cuscuta epithymum) that was

attacking a crop of carrots in a plastic tunnel in Co Wicklow. This is a parasitic

plant with no roots or leaves that coils itself around the host and is able to

extract the sap of the plant by means of suckers.

If you do come across an unusual weed and identify it correctly I’d encourage

you to report it to the National Biodiversity Data Centre via their website at

http://vascularplants.biodiversityireland.ie/.

4

Identifying seedlings

It can be difficult identifying weeds at the cotyledon stage as many of them

look rather similar. Things get a little easier as the first true leaves develop

and easier again when the flowers show. The only way to get good at weed

identification is by constant practice. A hand lens (x10) or magnifying glass can

be useful in identifying the finer points in weed ID. There is a list of weeds on

the very last page that you can print out and put on a clip board; practise ticking

off as many weeds as you can whenever you see them in a plot or field.

Seedling groups

Large cotyledons (1 cm) Hairy true-leaves

Ivy leaved speedwell Black nightshade

Charlock For-get-me-not

Cleavers Charlock

Thistle Hemp-nettle

Ivy leaved speedwell

Very small cotyledons (< 5 mm) Nipplewort

Groundsel Annual nettle

Annual nettle

Willowherb Very narrow cotyledons

Mouse ear chickweed Knotgrass

For-get-me-not Fumitory

Mayweed Common poppy

Corn spurrey

Notched cotyledons Swine cress

Deadnettle

Annual nettle Red hypocotyls

Hemp-nettle Redshank

Cleavers Knotgrass

Black bindweed

Round/oval cotyledons Fumitory (pink)

Field pansy Fat hen

Corn marigold

Sowthistle Strap shaped cotyledons

Common field speedwell Black bindweed

Sun spurge Fat hen

Thistle Orache

Nipplewort

Shepherd’s purse Pointed oval cotyledons

Annual nettle Chickweed

Deadnettle Mayweed/ Black bindweed

5

Seedling diagram

There are a few basic terms you need to

know when examining seedlings. The first

leaves you see are the seed leaves or

cotyledons. The next leavers formed are

the first true leaves which often look

different to the cotyledons. And

sometimes they can be different to the

subsequent leaves that develop. The

hypocotyl is that part of the stem below

the cotyledons.

When you see seedling weeds you’re

unsure of ask yourself the following:

Are the cotyledons very small or clearly visible?

Is the hypocotyl long or virtually non-existent? And what colour is it?

What shape are the cotyledons and is there anything distinctive about them?

Are the first true leaves smooth or hairy?

What colour is the seedling?

What adult plants are in the vicinity of the seedlings?

Examples: to identify chickweed I look for two things – colour (light green) and

pointed cotyledons. Annual nettle is very distinctive once it’s got its true leaves

(nettle like) but in the cotyledon stage note that it grows close to the ground

and has small seed leaves which have a characteristic dent at the apex.

Groundsel is very nondescript in the cotyledon stage but keep in mind they are

very small, and check the underside for a slight purple colouration. The same

trick can be used to tell orache and fat hen seedlings apart: purple below and it’s

fat hen, green below and its orache (mnemonic I use is GO!). Now, which cress is

this one? You’re thinking is this swine cress or its baby brother, lesser swine

cress? Just crush the foliage between your fingers and smell it – a distinct

cress smell means it’s lesser swine cress; little smell and it’s the other one. You

have a weed with very small oval cotyledons and a long narrow first leaf – then it

must be mayweed. This weed has fleshy cotyledons, waxy to the touch with a

well-developed hypocotyl – that’s corn marigold. You spot a seedling with the

longest seed leaves you’ve ever seen and they’re also very thin with a hint of

blue about them and a reddish tinge on the hypocotyl – you’re looking at

fumitory. To run down shepherd’s purse in the early plant stage, take out your

hand lens and check for star-like plant hairs. You see a distinctive notch at the

base of the cotyledons: that equals deadnettle. Fool’s parsley has long-oval,

somewhat pointed cotyledons with a characteristic deeply three-lobed first leaf.

6

Identifying weeds by flower colour

White Yellow

Shepherd’s purse Charlock

Swine cress Hedge mustard

Fool’s parsley Corn marigold

Scentless mayweed Groundsel

Chickweed Mayweed

Mouse-ear chickweed Sowthistle

Corn spurrey Colt’s foot

Black bindweed Field pansy

Cleavers

Black nightshade Blue

Speedwells

Pink/Purple For-get-me-not

Spear thistle

Creeping thistle Red

Fumitory Poppy

Hemp-nettle Redshank

Deadnettle Scarlet pimpernel

Willowherb

20 commonest arable weeds

1. Groundsel 11. Deadnettle

2. Annual meadow grass 12. Mayweed

3. Chickweed 13. Black bindweed

4. Shepherd’s purse 14. Fumitory

5. Fat hen 15. Speedwell

6. Orache 16. Charlock

7. Knotgrass 17. Hemp-nettle

8. Redshank 18. Sowthistle

9. Scutch 19. Annual nettle

10. Cleavers 20. Thistle

Acid soil weeds UK weeds not common in Ireland

Corn marigold Black grass

Hemp-nettle Bugloss

Redshank Green field speedwell

Corn spurrey Hen-bit deadnettle

Wild carrot

Wild radish/runch

Scented mayweed

7

APIACEAE (formerly UMBELLIFERAE) Crops: carrot, parsnip, celery, parsley, coriander

Fool’s Parsley – Aethusa cynapium (A)

This annual weed can be plentiful in a field but it’s only in the odd field that it’s

found. The common name certainly alludes to the fact that the foliage is very

similar to flat leaved parsley and could easily be mistaken for same – it’s also

rather similar to carrot foliage. It may also allude to the fact that it’s a

poisonous plant and only a fool would eat it. Fool’s parsley in the

seedling stage could be confused with creeping buttercup (see

right) but the narrower cotyledons and the distinctly three lobed

young adult leaf distinguish it. The image below shows it growing

in amongst parsley; one can see from the left hand image how

similar the leaf of Fool’s Parsley (arrowed) is to flat leaf parsley. The flat,

white, umbel type flower heads have characteristic downward pointing bracts.

Because it’s in the same family as carrots, parsnips, parsley and celery it can

become a problem weed in those crops. Tilled fields, gardens and waste places.

8

ASTERACEAE (formerly COMPOSITAE)

Crops: lettuce, salsify, chicory, endive, globe artichoke, Jerusalem artichoke

Creeping Thistle – Circium arvense (P)

More associated with pasture than tillage, creeping thistle can still cause

problems to the arable farmer in fields where it presents in large amounts. It’s

an abundant perennial weed that occurs in fields, waste ground and roadsides.

The main reason for its success as a weed is the extensive underground creeping

root system that rapidly forms dense patches. The development of horizontally

growing roots can spread the weed up to 6 m in a year. The deep-seated root

system is very brittle and easily breaks into pieces. Fragments of root from

plants in the field margins can be carried into the field and spread during

cultivation. Creeping thistle can also regenerate from seed but only about 3% of

it is viable. It flowers during July and August.

Thistle creeping in from the headland

9

Spear Thistle – Circium vulgare (B)

Spear thistle can appear just about anywhere – the airborne seeds which are

typical of this family can parachute into gardens, waste ground,

pasture, tillage fields and forestry plantations. It looks a bit like

creeping thistle but differs in a number of respects. First of all

it’s a biennial – it germinates and develops a low growing rosette in

year one and then in year two shoots up to over a metre tall,

flowers from July to October and dies off in the autumn. The

second difference is that while spread by seed is relatively

unimportant in creeping thistle, spear thistle’s sole method of

survival is by seed. And it can produce prodigious amounts – up to

8000 per plant. The image below shows the rosette stage.

Similar: the seedling stage looks similar to creeping thistle but the second true

leaf can be large with plenty of spines whereas creeping thistle has fewer

marginal spines. Both have large cotyledons.

Spear thistle Creeping thistle

X 1.5

Overwintering rosette stage

10

Corn Marigold – Chrysanthemum segetum (A)

Corn marigold is an attractive annual weed occasionally found in tillage fields and

waste places, usually on acid ground. The cotyledons are fleshy, hypocotyl is

long and the foliage is a waxy bluish-green colour. When in flower the large

bright yellow daisy like flowers are a dead giveaway.

Once abundant in corn fields it’s been decreasing in recent years due to

herbicide use and lime spreading. To quote from British Flora, Bentham and Hooker, 1905 : “‘A cornfield weed, probably of Mediterranean origin, but now

common all over Europe. Abundant in Britain”. Tilled fields, locally frequent in

the north, east and south, rather rare elsewhere.

Corn marigold growing in a

parsnip field near Skerries

Co Dublin on pH 5.6. Acid

indicator.

11

Groundsel – Senecio vulgaris (A)

Groundsel is an abundant annual tillage weed and once you get to know it, is a

distinctive weed in both leaf and general habit. However the very small

seedlings are less easy to identify except to say that the cotyledons are small

and narrow (1) and are frequently purple

underneath. The first leaves show the

characteristic serrations (2) that become even

more obvious later in life. Height varies anywhere

from 10-35 cm high. As you can see from the

table groundsel germinates, grows and flowers all

year around. An extremely successful weed.

Stand of groundsel

setting millions of seeds

in a crop of Brussels

sprouts. Seed germinates

at once if conditions are

wet. Can complete its

lifecycle in 5-6 weeks.

12

Mayweed (Pineapple weed) – Matricaria discoidea (A)

There are two mayweeds – mayweed (pineapple weed) and scentless mayweed –

the former much more common than the latter. They are difficult to distinguish

in the seedling stage but the first true leaves of mayweed have few or no lobes.

The feathery foliage is common to both but they are distinctly different when

in flower – mayweed has no petals and scentless mayweed has petals. Another

difference is alluded to in the common names of both – if you crush the foliage

between your fingers there is a strong smell (pineapple perhaps) from the

mayweed and no smell from the scentless mayweed.

Mayweed is an alien species possibly originating

in north-east Asia or north America, though now

well established throughout most of Europe. It

was first recorded in Co Dublin in 1894, probably

introduced with American corn fed to poultry.

Much of its rapid spread is thought to be due to

the seeds being carried on car tyres. It is a

common weed of footpaths, gateways, roadsides,

waste and arable ground and is very tolerant of

trampling. Abundant.

Similar: scentless mayweed as detailed above.

Could also be confused with swine cress in the

seedling stage, but the small cotyledons

distinguish it – swine cress has long narrow

cotyledons.

13

Scentless Mayweed – Tripleurospermum indorum (A)

Taller and much less common than its cousin mayweed, this species is attractive

when in flower during July to September. The first true leaf (arrowed) is lobed

in comparison to mayweed. In the adult stage the finely divided leaves combined

with large attractive daisy like flowers will guide you to the identification of

this species. Found on waste ground, roadsides and occasionally on arable

ground. Grows 30-80cm high. Occasional.

Similar: looks like mayweed as previously

described but the leaves are scentless and are

more finely divided.

The flowers are very similar to oxeye daisy

(Leucanthemum vulgare), a common wild flower,

but the leaves are completely different in the

two species; the leaves on the right are those

of oxeye daisy.

14

Prickly Sowthistle – Sonchus asper (A)

Though not quite so common as smooth sowthistle you won’t have too many

problems finding prickly sowthistle. Both species look somewhat alike but the

difference between the two lies in the common names – if you grasp common

sowthistle it’s smooth or soft to the touch whilst prickly sowthistle feels softly

sharp. The other key difference is the adult leaf bases – in prickly sowthistle

they are rounded, in common sowthistle they’re pointed. The leaf of the prickly

sowthistle is shiny and usually wavy whilst those of the common variety are a

slight bluish-green and flatter. Take note that the all the sowthistles have

downward pointing teeth on the leaf margin of the first true leaves.

Similar: smooth sowthistle, as above and the base of

the first true leaf is less cut away than with smooth

sowthistle.

Rosette stage

15

Perennial Sowthistle – Sonchus arvensis (P)

There are 3 sowthistles and this one is the least common of all – you’ll

occasionally find patches of it in tillage fields. It can be awkward to control with

selective herbicides as it comes equipped with an underground rhizome root

system. This allows it to persist in fields.

16

Smooth Sowthistle – Sonchus oleraceus (A)

This is an extremely common annual weed of disturbed ground and waste places.

Sometimes found in arable fields but not of great importance as a tillage weed.

The cotyledons are oval shaped and the first leaves are markedly cut away at

the base. The adult leaves are a dull bluish-green colour. The stem is hollow

and exudes a white sap if cut. Yellow dandelion like flowers are produced from

June to August.

Similar: could be confused with prickly

sowthistle but if you grasp this species the

leaves are sharp to touch whereas smooth

sowthistle is smooth to touch. Another

difference is the base of the clasping leaf –

smooth sowthistle has pointed ends

(arrowed), the prickly sowthistle has

rounded ends. Also similar to nipplewort in

the early plant stage but the leaves are

smooth not hairy.

Sowthistle

seedlings

17

Nipplewort – Lapsana communis (A)

Nipplewort is a common enough weed of waste

places, gardens and sometimes in arable situations

but doesn’t register too highly on the Richter

scale. An annual growing up to 75 cm it flowers

from June to September. The seedling is rather

nondescript and the yellow flowers can look rather

similar to other weeds of the same family such as

smooth sowthistle and hawkweed. But take note

that the early leaves are softly hairy to the touch

and appear singly – not in pairs. Upright habit.

Very frequent.

Cotyledons are oval to round, quite visible,

and the first true leaves have irregular

leaf margins with blunt points. It initially

develops as a rosette before shooting up

to flower.

Similar: could be confused in early growth

stages with smooth sowthistle but the

latter has totally smooth and hairless

leaves.

18

Colt’s Foot – Tussilago farfara (P)

This is a perennial weed that you more associate with rough ground and

roadsides but can occasionally become established in tillage fields. Local in

occurrence but can be a nuisance as it’s difficult to control with herbicides.

Associated with heavy, damp clay soils.

Whilst seedlings do occur most plants will arise from root fragments. Colt’s foot

also develops underground stems called rhizomes that spread the weed over a

wide area and subsequent cultivations can result in even greater dispersal.

The first leaves are broad, hairy and have teeth on the margins. Subsequent

leaves are large, angular and are covered with downy white hairs on the

underside of the leaf. The bright yellow flowers are distinctive in that they

flower in March and April before the leaves appear.

Growing on heavy Dublin soil Key feature: underside of the leaf is white

19

BORAGINACEAE

Forget-me-not – Mysotis arvensis (A)

We don’t have many blue flowered weeds – Forget-me-not is one of them. It’s an

annual or biennial plant that you’ll find on rough ground and the odd time in

arable situations, usually on dry, well drained soils. The cotyledons are small,

round, dark green and have the unusual feature of hairs. The seedling appears

to be close to the ground. Those that germinate late will overwinter as a

rosette. Key features are the dull hairy leaves and small blue flowers that

appear any time from April to August. Widespread and frequent but not a

problem in tillage fields – more of a garden weed.

Similar: in the seedling stage can be confused with mouse-ear chickweed - see

bottom of page 24 for differences. Also looks rather similar to the garden

variety, Mysotis sylvatica, which has been reported as a garden escape, but the

flowers of M. arvensis (3-4 mm) are smaller than those of M. sylvatica (6-8 mm).

20

BRASSICACEAE (formerly CRUCIFERAE) Crops: oilseed rape, cabbage, sprouts, cauliflower, broccoli, swede, radish, turnip, rocket

Charlock – Sinapsis arvensis (A)

If you are driving along in late spring and you notice a profusion of tall yellow

weeds at the side of the road, the likelihood is that they are charlock, wild

turnip (Brassica rapa) or occasionally oilseed rape. Charlock is a fairly distinctive

brassica weed that is commonly found in arable fields, gardens, roadsides and

waste places. It was a problem in cereals until the introduction of 2, 4-D after

the last war. And it’s still is a problem in brassicas especially in swedes where

there are no effective herbicides available to control it. It’s also responsible

for hosting a variety of brassica problems e.g. club root and cabbage root fly.

The seed leaves are very similar to cultivated brassicas and the

typical ‘brassica’ flowers don’t help much in identification but

the foliage is dark green and the leaves and stems are

rough to touch. It flowers from May to August.

Prefers heavy, calcareous ground. Frequent.

Similar: in the

young plant

stage can look

similar to

oilseed rape but

this species has

smooth leaves.

21

Shepherd’s Purse – Capsella bursa-pastoris (A)

Shepherd’s purse is a very common weed especially in vegetable brassicas. This

weed is not so easy to identify in its vegetative stage as you can get different

phenotypes – just a big word meaning different leaf shapes. The first few true

leaves are entire and later ones develop serrations or lobes. However the good

news is that it’s easy to identify when its characteristic triangular shaped seed

heads are formed. The flowers are small and white. Waste places, arable

ground and gardens. Abundant.

1. Cotyledons are small and oval.

2. First true leaves with star like hairs.

3. First true leaves with distinctive stalks.

Close-up of flowers. Brassica flowers always have four petals and are usually white or yellow in colour.

22

Swine Cress – Coronopsus squamatus (A)

Swine cress is an occasional weed particularly in coastal counties that you’ll come

across in trampled ground conditions such as pathways, gateways and around

cattle troughs but also on waste ground and sometimes in tillage fields

particularly along the coast. It’s quite common in Co Dublin arable ground but

never in large numbers.

It has a little brother called C. didymus, lesser swine cress, an annual weed from

South America that’s on the increase in this country particularly in the southern

half. However not often seen in tillage fields – more usually found in rough

ground areas. Both look rather similar but there are a couple of defining

differences. The foliage of swine cress is broader - see image above. In flower

you’ll notice that swine cress has very small (2-3 mm) but visible white flowers,

the lesser version has no petals and are difficult to see. If there are no flowers

present just crush the foliage between your fingers – lesser swine cress has a

pungent cress smell, swine cress doesn’t.

Similar: could confuse these two with

the mayweeds in the seedling to young

plant stage but the long swine cress

cotyledons distinguish them.

Characteristic notch on the top of the fruit of lesser swine cress

23

Hedge Mustard – Sisymbrium officinale (A)

Hedge mustard is a common plant of hedgerows, road sides and waste places but

less often in arable ground. When you do find it in tillage fields it’s usually

growing on headlands or close to the ditch.

It is an annual or over wintering annual and the image below shows a late

germinating plant in the rosette stage. In the springtime it will shoot up to 30-

70 cm tall to flower and set seed. It’s a very distinctive weed in the seed stage

as the small yellow flowers develop into seed heads that are pressed close in to

the stem. Another feature to note is the flowering shoots grow at right angles

to the main stem.

24

CARYOPHYLLACEAE

Mouse-ear Chickweed – Cerastium fontanum (P)

This is a common wild flower that can occur in tillage fields but is a low growing,

and largely inoffensive weed; not a problem. It has a loosely tufted appearance

when young and later develops a sprawling habit with ascending flower heads.

Widespread and common in grassland, waste places and cultivated ground.

It is a perennial plant by nature but acts as an annual in arable crops as it comes

readily from seed. The cotyledons are very small and hairless and the adult

leaves are hairy to the touch. The white flowers have distinctly notched petals.

Similar: could be confused with forget-me-not in the small plant stage but the

leaves of common mouse-ear are opposite on the stem and forget-me-not are

alternate – see image below. Opposite leaves appear together when they are

young, equal in size, whilst alternate leaves appear singly one after another and

are different in size.

X 1.5

25

Chickweed – Stellaria media (A)

Chickweed is everywhere. It seemingly pops up every time you disturb the soil.

You’ll even see it growing alongside walls, on top of walls, cracks in pavements

and sometimes will attempt to secure a toe-hold in lawns and grassland if there’s

a bit of bare ground within those habitats. The leaves and seeds are eaten by

birds – hence its ability to spread widely. One of the commonest weeds of arable

fields and gardens. Abundant.

It has two main germination phases – spring and autumn - the cotyledons are a

light pale green, held well off the ground, are oval in shape and pointed at the

ends. Chickweed has shallow, fibrous roots which make it easy to hand weed.

The plant's weak stems mostly trail along the ground and in fertile, friable

ground can choke plants or a crop as it spreads e.g. autumn sown scallions. The

stems branch very frequently and take root at the leaf junctions. If you look

very closely at the stems, you'll see a single line of hairs running up the side, and

you'll notice that the line changes sides at each leaf junction. The small white

flowers can be seen every month of the year; it’s a prodigious seeder – up to

15,000 per plant.

It will as happily grow in shaded areas as out in the open and can be found over a

range of pH’s except in very acidic soils.

Chickweed can flourish in the cooler, damper

conditions of autumn – seen here doing its best

to choke a crop of leeks.

Similar: common mouse ear but that has a

hairy leaf.

26

Corn Spurrey – Spergula arvensis (A)

You will occasionally come across this weed, especially on light, acid ground. It is

quite a distinctive weed with its long, thin cotyledons followed by equally long,

thin adult leaves arranged in whorls. Up to two generations a year occur as seed

can be set within 10 weeks of germinating. It’s in flower from June to

September and the small white flowers open for 3-5 hours per day from noon

onwards. It’s not a problem weed as most of the herbicides used in cereal crops

can control it.

Growing in the Bog of the Ring Co Dublin on acid ground

27

CHENOPODIACEAE Crops: beetroot, spinach, Swiss chard

Two weeds in this family concern us: fat hen and orache. Both are very common

annual weeds often found growing side by side. One can get confused between

them as they look rather similar but there are differences to help tell them

apart. These weeds germinate during the spring and summer – you won’t see

them in the winter.

Fat Hen – Chenopodium album (A)

Fat hen or lamb’s quarters is a common annual tillage weed that

can grow as high as a house in rich ground if you let it. However

seedlings that appear in late summer will only form small plants.

The seedling has strap shaped seed leaves with a distinctive

purplish colouration on the undersides (see image above). The

other characteristic of fat hen is its upright habit

and the leaves are alternate and mealy (especially

the youngest ones). Mealy is the term for the

visible wax layer on the leaf that gives a silvery look

to them. Fat hen always keeps this mealy

appearance right to the end – the flower heads look

silvery in colour while the orache flower heads have a reddish

hue to them. Fat hen was eaten as a vegetable from Neolithic

times until the 16th century when it was replaced in the diet by

spinach and cabbage. Abundant.

Similar: orache – see comments above.

28

Orache – Atriplex patula (A)

The orache cotyledons are similar in shape to fat hen but are green underneath

rather than purple. The other common name of orache is creeping fat hen and

this is a dead giveaway in distinguishing the two – if you come across large fat

hen and orache growing side by side you’ll plainly see the side shoots of orache

sprawling on the ground as against the much more upright habit of fat hen.

Other distinguishing features of orache are the little points at the base of the

first true leaves and you may notice a slight redness to the edge of the leaf.

The leaves are opposite each other rather than alternate as in fat hen.

It flowers from July to September and the seeds can last in the soil for up to

30 years. You will note from the graphs that orache doesn’t germinate as late in

the season as fat hen. Tends to avoid the more acid soils. Frequent.

Similar: fat hen – see comments above.

Typical sprawling growth of orache

29

EUPHORBIACEAE

Sun Spurge – Euphorbia helioscopia (A)

You’ll find this weed in tilled ground and waste places. Quite commonly seen in

vegetable fields but it never develops into a weed problem as it doesn’t grow in

stands. It tends to be single stemmed, but sometimes branched at the base,

growing to 20-45 cm high – a taller and larger plant than petty spurge which is a

common garden species. If you break the stem you get a characteristic white

sap exuding. Seen above growing in a crop of scallions. Very frequent.

Cotyledons long oval in shape often with brown markings –

would remind you of a running track.

First true leaves are oval in shape and have small serrations

towards the tip of the leaves, unlike petty spurge which are

smooth.

Cotyledons are purple underneath.

Similar: petty spurge (E. peplus), smaller in all its parts and the main stem

divides into 3 flowering stems; sun spurge divides into 5 flowering stems.

30

LAMIACEAE (formerly LABIATAE)

Crops: mint, sage

This family has one very unique feature: if you roll the stem between your

fingers – it’s square. It contains three weeds – deadnettle, hemp-nettle and

marsh woundwort.

Hemp-nettle – Galeopsis tetrahit (A)

Hemp-nettle is an occasional arable weed that crops up in spring cereals and

vegetable crops, particularly on the more acidic soils. Possibly found more

frequently on damper sites. Not a problem weed as most of the herbicides will

control it. It’s a spring germinator with large cotyledons that have backwardly

pointing lobes. The leaves have distinctly regular veining and the plant has a

coarse bristly feel to it. A key feature is a swelling of the stem (square in

shape) where the leaves join it. It flowers from July to September. It’s a

species that may be declining in occurrence.

31

Deadnettle – Lamium purpureum (A)

This common annual weed is easy to recognise in the

seedling stage with its round notched seed leaves, the

early leaves that are similar to the adult ones, and the

square stem of the older plant, typical of the Lamiaceae

family. You get large numbers of seedlings in the

autumn. Purple flowers. The leaves somewhat resemble

a nettle but don’t sting, hence the name deadnettle. Found in waste places and

tilled areas. Frequent.

1. Vertical hypocotyl and horizontal

cotyledons make it stand away from the

ground.

2. Distinctive notch at base of cotyledon.

3. First true leaves evenly notched, with

prominent branched veins, hairy.

Marsh Woundwort – Stachys palustris (P)

This species occurs occasionally as a weed in arable land and

is associated with damp ground. It’s an erect, hairy,

rhizomatous perennial up to a metre high. The short stalked

leaves distinguish it from the rather similar Hedge

Woundwort (Stachys sylvatica) which has stalked leaves.

32

ONAGRACEAE

Willowherb, broad leaved – Epilobium montanum (P)

Willowherb is a common plant in Ireland and there

are quite a few different species that can be a bit

confusing to tell apart. They all share one thing in

common – the seed is spread by the wind and this

means they tend to be widespread. Broad leaved

willowherb can be found everywhere: cities, woods,

waste ground, gardens, nurseries and on arable

ground. Whilst it commonly appears in tillage

fields it’s not a problem weed. Often seen in

stubbles.

How do you tell this species apart from the other two common ones,

American willowherb and hoary leaved willowherb? As the name

suggests the leaves are broad, opposite and smooth. The pinkish

mauve flowers are about 1 cm across and the stigma is 4 lobed. It

tends to favour neutral to calcareous conditions.

1. The cotyledons are very small and lie

close to the ground. So small in fact

that you won’t normally notice them.

2. The first true leaves are shiny,

yellowish green and lie close to the

ground.

33

PAPAVARACEAE

Poppy, common – Papaver rhoeas (A)

Long associated as a cereal weed, the striking red flowers of

the poppy make this one easy to recognise. In flower from

June to September with the flowers lasting a day or two

before the petals drop off and blow away. It’s a prodigious

seeder with up to 20,000 seeds per plant. The seed need

light to germinate and is a shallow germinator. They can last

for a 100 years in the soil until brought to the surface by

cultivation or soil disturbance. Hence the appearance in

their multitudes on the battle scarred terrain of Flanders

and The Somme in World War 1. For similar reasons you’ll

also see them appear alongside new roads just after they are

built. It has two periods of germination – spring and autumn

and is more of a weed in cereals than vegetables. Frequent in

the south, centre and east, rarer in the west and north.

Similar: the coarse spreading hairs on the flower stem

distinguish the common poppy from P. dubium where the hairs

are not spreading and the

flower is light red in colour

rather than bright red. The

rosette stage is a little

similar to shepherd’s purse

but hairs are single and not

star shaped – you’ll need a

hand lens to see this feature.

34

Fumitory

There are three species of fumitory found in tillage fields, gardens and on waste

ground: F. officinalis, F. muralis and F. bastardii. The latter two species look

very similar. But most people just refer to them as fumitory. They all share the

characteristic long narrow pointed seed leaves and the feathery foliage - would

remind you of carrots and certainly when you see fumitory just germinated in a

row of germinating carrots you have to check twice to differentiate the weed

from the crop. The three species can be identified apart when in flower. Common fumitory – Fumaria officinalis (A)

This is a common weed of arable land and

gardens, particularly on light soils. Its foliage

is feathery in shape and is distinctly darker

more blue-green in colour than the leaves of

common ramping fumitory. The flower length is

also smaller – less than 1 cm. Note also the

lower petal of the flower – it’s spoon shaped.

Tall ramping fumitory – Fumaria bastardii (A)

This species is distinguished from F. officinalis by

the larger distinctly purple tipped (>1 cm) flowers

that have a lower petal with parallel sides . The

foliage is broader with less of a feathery look to it

and is lighter green in colour. Fumaria bastardii is

difficult to distinguish from F. muralis.

35

POACEAE Crops: wheat, barley, oats, rye, millet, maize, rice, sugar cane

Hugely important family as it contains the cereals that supply a large proportion

of the food we eat. It also contains a number of species that are weeds and

because they are in the same family as cereals can be difficult to control in

these crops. The most common grass weeds in cereals include scutch, annual

meadow grass, wild oats and to a lesser extent rough stalk meadow grass. Canary

grass is an increasing threat and sterile brome can cause problems in min-till

crops. Grasses are known as monocots, which mean that they only have one

cotyledon unlike the rest of the broadleaved weeds which have two.

Annual Meadow Grass – Poa annua (A)

Annual meadow grass is an abundant tillage weed that can be found at any time

of the year in virtually all fields. It’s probably the most widespread wild grass in

the world. It’s a tufted annual or short lived perennial, usually quite low growing.

What it lack in scale it makes up for in numbers: huge amounts can germinate to

give a mat of grass that can be quite competitive with crop growth.

It has light green hairless leaves that

are flattened with a curved tip (boat

shaped). The underside of the leaf has

a central ridge, with tramlines on the

upper surface. You will need a hand

lens to observe these leaf features

clearly. It flowers all year round and

can complete its lifecycle in as short a

period as 6 weeks.

36

Scutch Grass – Elymus repens (P)

Scutch grass which is referred to as couch in the UK is a very common weed of

tillage crops. If allowed to establish it can become very competitive with all

crops. Fortunately there are some very effective grass herbicides available to

control it.

This is a perennial grass with vigorous underground stems called rhizomes which

if broken up will readily regrow – see right-hand image below. The leaves are a

dull green in colour, somewhat broad and the leaf is slightly rough to the touch

if you pull the blade backwards between your fingertips. The ligule (black

arrow) is very short (1 mm – hard to see!) and the auricles (red arrow) are short

and pointed. It does flower but doesn’t set a lot of viable seed and mostly

spreads vegetatively through the growth of its rhizomes. Mature shoots die

back in the late autumn but young shoots can overwinter.

Similar: could be confused

with a far less common grass

weed called Black bent

(Agrostis gigantea) which also

has rhizomes, or creeping

bent (Agrostis stolonifera)

which has stolons.

37

Wild Oats – Avena fatua (A)

Wild oats began to become a problem in the

1970’s in cereal crops and has increased to

such an extent that it’s now a common and

serious weed in cereals. In fact it’s the only

annual weed that’s listed under the various

Noxious Weeds Acts.

The first thing to look out for when you’re

checking cereal fields for wild oats, are any

cereal-like plants growing between the rows.

And if trying to identify between wild and

cultivated oats here are the differences: the

leaf of the wild oat is hairy, darker green and

it twists in an anti-clockwise direction as

opposed to the opposite traits in cultivated

oats.

The lack of auricles (red arrow), is the

difference between oats versus wheat (small

hairy auricles) or barley (large hairless

auricles – black arrow).

38

POLYGONACEAE

Crops: rhubarb

This family includes the docks and three common tillage weeds – knotgrass,

redshank and black bindweed, all of which have red coloured hypocotyls.

Black Bindweed – Fallopia convolvulvus (A)

This is a common, annual, twining weed, which can choke crops if left unchecked.

The flowers are insignificant, typical polygonums, not much to look at, so we’re

left with the leaves for ID purposes. Don’t confuse them with the Convolvulus

species, as they look similar and hence the common name reference of black

bindweed and indeed the specific name convolvulus. The characteristic feature

is a leaf with three pointed lobes – spear shaped. Very frequent.

Similar: the cotyledons could be confused with those of redshank as both have

red hypocotyls but the seed leaves of black bindweed are long rather than the

more oval redshank cotyledons. Once the first true leaf appears identification

is much easier as it has the typical black bindweed leaf. Also field bindweed,

which is uncommon in tillage, has a more rounded apex to the leaf.

39

Knotgrass – Polygonum aviculare (A)

Knotgrass is a tough as old boots weed that is equally at home in the city centre

surviving between paving cracks or luxuriating in a cereal field in the middle of

the countryside. This is an annual weed that can grow to quite a size if it’s let

and unlike redshank is just at home on alkaline ground as acidic. Can be difficult

to control with herbicides beyond the young plant stage. Abundant.

The key ID features are a red coloured hypocotyl (usually) and very thin

cotyledons with a first leaf that could be confused with redshank – but look for

the thin seed leaves.

Similar: redshank in the young

seedling stage.

Growing in hard ground at a gateway

The three

polygonums can

often be found

growing together

and can be

distinguished

apart from the

shape of their

cotyledons and

first true leaves.

From top down:

Knotgrass

Redshank

Black bindweed

40

Redshank – Polygonum persicaria (A)

If ever there was a weed designed to smother a crop, redshank is it. It can

germinate en-masse to give a sea of redshank covering an entire area, and end up

half a metre tall with the crop disappeared from view. It’s a species associated

with damp, acidic soils but is frequently found on well drained ground as well. It

is interesting to note that it’s one of the few tillage weeds absent from the very

alkaline soil of Kinsealy. It’s a common weed in arable situations. It germinates

in the spring and early summer with the seedlings having a distinctive red

hypocotyl with oval dark green seed leaves . The mature plant can easily be

recognised with the dark blotch in the centre of the leaf. The only other

species that looks similar is the much less common pale persicaria (P. lapathifolium) which doesn’t have a blotch and can be found side by side with

redshank. I have often noticed redshank germinating in crops after ploughing up

old ley – seeds must be long lived. Abundant.

41

RUBIACEAE

Cleavers (Robin-run-the-hedge) – Galium aparine (A)

Cleavers is an annual weed that’s commonly found in both gardens and arable

areas and is very competitive, especially in cereals. It’s often found near the

margin of tillage fields where it moves out from the hedgerow. Can be an

awkward weed with an ability to smother out a crop plus its resistance to a

number of herbicides. Cleavers is distinctive in several ways. It’s unusual in that

it starts to germinate in the autumn from September on, right through to

spring. It has large seed leaves notched at the end and the subsequent adult

leaves are produced in whorls, which look unlike any other weed. If you examine

any part of the stem, leaf or seed closely you’ll see them covered in tiny barbs

(see image below) – this is a dispersal mechanism for the seed as they can hook

onto animals passing through. They also allow the plant to clamber up

others and get its head into the light.

Similar: ivy leaved speedwell in the cotyledon stage but

no notch and cleaver is a stouter seedling. Also

Sherardia arvensis (field madder) looks a little like a

mini-cleavers but smaller leaves and tiny pinky-mauve

flowers distinguish it; but rarely found on arable land.

42

SCROPHULARIACEAE

There are two species of speedwell that you’ll come across in tillage situations –

common field speedwell and much less commonly, ivy leaved speedwell.

Common Field Speedwell – Veronica persica (A)

If you come across a weed with blue flowers in a tillage field or vegetable

garden the likelihood is that it’s this species – common field speedwell. As you

can see from the chart it germinates and flowers throughout the year. The

cotyledons are shovel shaped, medium size and the first true leaf margins are

shallowly and regularly notched and hairy. It has a sprawling habit, with large

flowers on long stalks – well, large in comparison to the other veronica species.

The leaves are light green in colour. Abundant.

This species is native to south-west Asia and first appearing in Europe around

the 1800’s. Irish records suggest that it arrived here prior to 1845 somewhere

near Cork and was well established by the end of the 19th century.

Similar: the leaves on ivy leaved speedwell are dark green in colour.

43

Ivy Leaved Speedwell – Veronica hederifolia (A)

The Ivy leaved speedwell is more likely to be found in the garden than the field.

Two things to point out about its early life – size of seed leaves and time of

germination. If you see a weed seedling with large cotyledons on long stalks in

the autumn or winter, think cleavers or ivy leaved speedwell; it’s a bit unusual in

that it germinates from October to April. If you see V. hederifolia growing

alongside V. persica the ivy leaved version is darker green and the common field

speedwell is a lighter green in colour. In comparison to the field speedwell the

flowers are small, not that noticeable.

Similar: the large cotyledons could cause confusion with

cleavers, which are of a similar size and shape. However

the cotyledons on cleavers have a distinctive notch at

the apex and the hypocotyl is thicker and more robust.

Leaf shape as an aid to

identification can help and also

confuse. The leaf of the ivy leaved

speedwell is distinctly lobed in

comparison to common field

speedwell. But the smaller (younger)

leaf of common field speedwell is very similar to that of red deadnettle and

both are hairy. But one can tell them apart as the venation of the deadnettle is

much more distinct and pronounced than that of the speedwell (unfortunately

not evident from the image above).

44

SOLANACEAE Crops: potato, tomato, sweet pepper, chilli pepper, aubergine

Black Nightshade – Solanum nigrum (A)

Black because of the small black berries of this poisonous weed. All parts of the

plants are potentially poisonous with the highest concentration in the unripened

berries. I did hear of a case where nuns consumed the ripened fruit with no ill-

effects. Divine intervention perhaps.

There is probably a heat requirement with this

species as it is commonly found growing in old

glasshouses and is associated with maize especially if

it’s grown under plastic. It also shows up in maize

because nightshade is a late germinating weed. The

cotyledons are sharply pointed and hairy. Being a

member of the potato family it’s hardly surprising

that nightshade looks a little

potato-like in its appearance. The

white potato-like flowers is also a

key diagnostic feature. Take note

that potato crops can the odd

time produce fruit which germinates the following year; don’t

confuse them with nightshade seedlings. An occasional annual

mostly seen in the south and east of the country.

Similar: – potato seedlings as detailed above; you may come across bittersweet

(S. dulcamara) in hedgerows and waste places. It’s a pretty common shrubby

type species with purple flowers and red fruits.

45

URTICACEAE

Annual Nettle – Urtica urens (A)

Every kid recognises nettles and wasps – they can both give you an unpleasant

sting. Nettles are covered with tiny, nearly invisible stinging hairs that produce

an intense, stinging pain, followed by redness and skin irritation. The generic

name comes from the Latin word, ‘uro’, which means ‘I burn’. There are two

species: common nettle, a perennial found in grassland or waste ground and

annual nettle, found in arable fields. It’s extremely common on the rich, sandy,

horticultural soils in Rush Co Dublin; but is found on heavier soils too,

particularly those associated with market gardening. Annual nettle is a prolific

seeder – it starts shedding seeds from four weeks old and will continue to do so

until the winter frosts arrive.

It germinates from spring right through to autumn. The characteristic features

at the germination stage are: the seed leaves are small and close to the ground,

the apex of the seed leaf is notched and the first true leaf is very noticeably

that of a nettle. The adult leaves look very similar to those of the common

nettle except for one key difference – the base of the annual nettle is V shaped

and the base of the perennial nettle is heart shaped. The other difference is

size of plant; annual nettle is a lot smaller

than the common nettle.

Similar: in the seedling stage, the more pointed

teeth on the first true leaf of annual nettle

distinguish it from perennial nettle, shown here with

the right-hand second true leaf missing. Subsequent

leaves of both are very similar. The seed leaf of

annual nettle is longer than perennial nettle.

46

VIOLACEAE

Field Pansy (Heartsease) – Viola arvensis (A)

As the specific name suggests (arvensis = arable land) this is the pansy you’ll

find growing on tillage ground. As a weed it doesn’t grow aggressively and is

quite small in stature, so it normally doesn’t cause big problems in crops. It’s a

pretty distinctive weed that you may occasionally come across – it’s certainly not

found everywhere. It’s distinctive because it looks so like the familiar garden

pansy, creamy white flowers with a yellow eye and the first true leaves have

broadly rounded edges. Frequent in the south, east and north east, occasional

elsewhere.

Similar: looks similar to the much less frequent

wild pansy (V. tricolor) but the flowers of this

species are violet-blue, cream in colour with the

petals longer than the sepals.

Is this plant Viola tricolor?

47

List of illustrated weeds by family:

Apiaceae: Fool’s parsley

Asteraceae: Creeping thistle, spear thistle, colt’s foot, corn marigold, groundsel,

mayweed, scentless mayweed, smooth sowthistle, prickly sowthistle,

perennial sowthistle, nipplewort

Boraginaceae For-get-me-not

Brassicaceae: Charlock, shepherd’s purse, swine cress, hedge mustard

Caryophyllaceae: Chickweed, corn spurrey, mouse-ear chickweed

Chenopodiaceae: Fat hen, orache

Euphorbiaceae: Sun spurge

Lamiaceae: Hemp-nettle, deadnettle, marsh woundwort

Onagraceae Willowherb

Papavaraceae: Common poppy, fumitory

Poaceae: Annual meadow grass, scutch, wild oats

Polygonaceae: Black bindweed, knotgrass, redshank

Rubiaceae: Cleavers

Scrophulariaceae: Common field speedwell, ivy leaved speedwell

Solanaceae: Black nightshade

Urticaceae: Annual nettle

Violaceae: Field pansy

Sources, acknowledgements and thanks:

Webb’s An Irish Flora, John Parnell and Tom Curtis

The Wild Flowers of the British Isles, Ian Garrard and David Streeter

ADAS Colour Atlas of Weed Seedlings, JB Williams and JR Morrison

Weeds in Sugar Beet, Agrevo

The Identification of Weed Seedlings of Farm and Garden, RJ Chancellor

Flora of County Dublin, Dublin Naturalists Field Club

A Catalogue of Alien Plants in Ireland, Sylvia Reynolds

British Flora (1905), Bentham and Hooker

The Arable Weeds of Europe, Martin Hanf

Weed Guide, Bayer Crop Science

Encyclopaedia of Arable Weeds, HGCA

Two recommended website are:

http://web.adas.co.uk/WeedManager.

Irish Wildflowers – www.irishwildflowers.ie

Stephen Alexander

Teagasc , Co Dublin

Weed survey

Fie

ld n

am

e

%

Annual meadow grass

Annual nettle

Black bindweed

Black nightshade

Buttercup

Charlock

Chickweed

Cleavers

Colt’s foot

Corn marigold

Deadnettle

Dock

Fat hen

Fool’s parsley

For-get-me-not

Fumitory

Groundsel

Hedge mustard

Hemp-nettle

Knotgrass

Mayweed

Mayweed, scentless

Mouse-ear chickweed

Orache

Pansy

Poppy

Redshank

Scarlet pimpernel

Scutch

Shepherd’s purse

Sowthistle, common

Sowthistle, prickly

Sowthistle, perennial

Speedwell, field

Speedwell, ivy

Spurrey, corn

Sun spurge

Swine cress

Thistle, creeping

Thistle, spear

Volunteer cereals

Volunteer oilseed rape

Wild oats

Willowherb